Optic Chiasm Width in Normal-Tension and High-Tension Glaucoma

Purpose: The aim of our study was to find out whether in patients with hypertensive glaucoma (HTG) and normotensive glaucoma (NTG), there is a change in the size of the chiasm depending on the changes in the visual field. Therefore, we retrospectively measured the width of the chiasm in the patients to whom we measured the size of the corpus geniculatum laterale in 2013. Materials and methods: The group consisted of two groups of patients. Nine with hypertensive glaucoma (HTG) and nine with normotensive glaucoma (NTG). The diagnosis was based on a complex ophthalmological examination and in NTG and electrophysiological examination. The visual field was examined by a rapid threshold program on the Medmont M700. The sum of the sensitivity from both visual fields in the range of 0-22 degrees was compared with the width of the chiasm obtained by the magnetic resonance imaging using the eight channel head coil. The measured values of all subjects were analyzed using a paired t-test and a correlation coefficient. Results: We found a reduction in the chiasma width in both glaucoma groups. We found a statistically significant difference in the size of the chiasm (p = 0.0003) between the control group and the HTG group (p = 0.001). The narrowing of the chiasm showed a slight correlation in HTG with changes in the field of vision (r = 0.139) and in NTG a moderate correlation (r = 0.375). Conclusion: We found a reduction in the size of the chiasm in both HTG and NTG. The sum of sensitivities in the central parts of the visual field, however, more correlated with the reduction in the size of the chiasm in NTG. This finding shows that there are two different diagnostic groups.

Responses to Moving Visual Stimuli in Pretectal Neurons of the Small-Spotted Dogfish (Scyliorhinus canicula)

Single-unit recordings were performed from a retinorecipient pretectal area (corpus geniculatum laterale) in Scyliorhinus canicula. The function and homology of this nucleus has not been clarified so far. During visual stimulation with a random dot pattern, 45 (35%) neurons were found to be direction selective, 10 (8%) were axis selective (best neuronal responses to rotations in both directions around one particular stimulus axis), and 75 (58%) were movement sensitive. Direction-selective responses were found to the following stimulus directions (in retinal coordinates): temporonasal and nasotemporal horizontal movements, up- and downward vertical movements, and oblique movements. All directions of motion were represented equally by our sample of pretectal neurons. Additionally we tested the responses of 58 of the 130 neurons to random dot patterns rotating around the semicircular canal or body axes to investigate whether direction-selective visual information is mapped into vestibular coordinates in pretectal neurons of this chondrichthyan species. Again all rotational directions were represented equally, which argues against a direct transformation from a retinal to a vestibular reference frame. If a complete transformation had occurred, responses to rotational axes corresponding to the axes of the semicircular canals should have been overrepresented. In conclusion, the recorded direction-selective neurons in the Cgl are plausible detectors for retinal slip created by body rotations in all directions.

The Arrangement of Corpus Geniculatum Laterale Connections with Oculomotor Structures

The primary visual centres are known to be involved in the organisation of oculomotor acts, but the pathways of signal transmission from corpus geniculatum laterale (lateral geniculate nucleus, LGN) to the structures of the oculomotor system remain unknown. The aim of this study on 30 cats was to determine autoradiographically all the possible pathways of visual information transmission from both dorsal and ventral nuclei of the LGN to oculomotor nuclei. It was found that there were no direct connections of the LGN with the oculomotor nucleus. The connection occurs either through the cortex or through the preoculomotor formations. These pathways are the following: (1) from the dorsal and ventral nuclei of the LGN to the visual pretectum (olivary pretectal nucleus, posterior pretectal nucleus, nucleus of the optic tract) and then to the vegetative part of III nucleus or through nucleus commissurae posterioris, Cajal and Darkschewitsch nuclei to the somatis part of III nucleus and along the medial longitudinal fasciculus to IV nucleus and periabducens region; (2) from the ventral LGN into the deep layers (IV and VI) of the superior colliculus, and then to the Edinger - Westphal nucleus, preoculomotor central gray substance, and VI nucleus; (3) from the dorsal LGN into the deep layers (IV and VI) of the superior colliculus with relay synapses in the parietal cortex and zona insecta; (4) from the dorsal and ventral nuclei of the LGN to nucleus pontis dorsolateralis and paramedianus, being connected with the vermis anterior lobe (V - VII lobes) of cerebellum, and then to nucleus vestibularis inferior and nucleus vestibularis lateralis.